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TCA9555: TCA9555 I/O design questions

user4979899
Expert 3080 points
Part Number: TCA9555
Other Parts Discussed in Thread: TCA9535

Hi Sir,

When we use GPIO mode to enable/disable device(default is disable device) how to connect this I/O pin at power on configure as an input??

 

 

  • 0
    TI__Guru* 77571 points
    Hey Anne,

    When TCA9555 turns on it is an input referenced to Vcc due to the 100k pull up resistor.

    This means you do not need to configure the device to be an input as it already starts up as an input when it is turned on. If you need to, you can set a pull down resistor on the pin if you would like the pin to be referenced to GND upon start up.

    Does this answer your question or do you need clarification on something else?

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    TI__Expert 3080 points

    Thanks Bobby,

    And how about the TCA9535?

    When we use gpio to enable/disable device(default is disable device) how to connect this pin at power on configure as an input??

  • 0 in reply to user4979899
    TI__Guru* 77571 points

    Hey Anne,

    TCA9535 also starts up as an input but is HI-Z (no internal pull up like you pointed out). You can either reference the pin with a pull up or pull down resistor depending on your preference. So in your example, you want to keep the device tied to a GPIO as a default disable therefore if GND keeps the device disabled then you would tie the GPI to GND.

    I hope this makes sense.

    Thanks,

    -Bobby